Sources and Docs: Fix typos and nxstyle issues

Documentation/contributing/coding_style.rst:

    * Fix repeated words: ("this this").
    * Remove trailing spaces.

boards/z80/z80/z80sim/README.txt:

    * Fix repeated words: ("this this") and rewrap lines.

graphics/Kconfig,
libs/libc/math/Kconfig:

    * Fix repeated words: ("this this").

arch/arm/src/armv7-a/arm_assert.c,
arch/arm/src/armv7-r/arm_assert.c,
arch/arm/src/imxrt/imxrt_enet.c,
arch/arm/src/kinetis/kinetis_enet.c,
arch/arm/src/kinetis/kinetis_flexcan.c,
arch/arm/src/s32k1xx/s32k1xx_enet.c,
arch/arm/src/s32k1xx/s32k1xx_flexcan.c,
arch/arm/src/stm32/stm32_pwm.c,
arch/arm/src/stm32h7/stm32_pwm.c,
arch/arm/src/stm32l4/stm32l4_pwm.c,
arch/renesas/src/rx65n/rx65n_usbdev.c,
binfmt/libnxflat/libnxflat_bind.c,
drivers/pipes/pipe_common.c,
net/igmp/igmp_input.c,
net/tcp/tcp_conn.c,
sched/sched/sched_roundrobin.c:

    * Fix typo in comment ("this this").

arch/arm/src/cxd56xx/cxd56_usbdev.c,
arch/arm/src/lc823450/lc823450_usbdev.c:

    * Fix typo in comment and rewrap lines.

arch/arm/src/imxrt/imxrt_usbdev.c,
arch/arm/src/stm32/stm32_dac.c,
arch/arm/src/stm32f0l0g0/stm32_pwm.c,
arch/arm/src/stm32f7/stm32_pwm.c,
arch/arm/src/tiva/lm/lm4f_gpio.h,
fs/nxffs/nxffs_write.c,
include/nuttx/analog/pga11x.h,
include/nuttx/usb/usbdev.h,
net/mld/mld_join.c:

    * Fix typo in comment ("this this").
    * Fix nxstyle issues.

binfmt/libnxflat/libnxflat_bind.c

@@ -454,7 +454,7 @@ static inline int nxflat_bindimports(FAR struct nxflat_loadinfo_s *loadinfo,
           symname = (FAR char *)
             (offset + loadinfo->ispace + sizeof(struct nxflat_hdr_s));
 
-          /* Find the exported symbol value for this this symbol name. */
+          /* Find the exported symbol value for this symbol name. */
 
 #ifdef CONFIG_SYMTAB_ORDEREDBYNAME
           symbol = symtab_findorderedbyname(exports, symname, nexports);