examples: fix building on arm32

Refer to the commit a3c101a ("examples: fix building on arm64")
fix for arm32. crt0.S does not even build with:
    operating system and architecture:
        5.15.0-130-generic x86_64
    installed version of gcc and binutils:
        gcc version 9.4.0 (Ubuntu 9.4.0-1ubuntu1~20.04.3)
    GNU ld (GNU Binutils for Ubuntu) 2.34
    used defconfig:
        stm32h750-art-pi_defconfig
    used commands for building:
        export CROSS_COMPILE=arm-none-eabi- ARCH=arm
        make stm32h750-art-pi_defconfig
        make menuconfig # to add
        make
    examples/api/crt0.S: Assembler messages:
    examples/api/crt0.S:32: Error: lo register required -- `ldr ip,=search_hint'
    examples/api/crt0.S:33: Error: lo register required -- `str sp,[ip]'
    examples/api/crt0.S:39: Error: lo register required -- `ldr ip,=syscall_ptr'
    examples/api/crt0.S:40: Error: lo register required -- `ldr pc,[ip]'
    make[2]: *** [scripts/Makefile.build:292：examples/api/crt0.o] Error 1

Use valid register names and instructions.

Signed-off-by: Liya Huang <[email protected]>

Author: wdfk-prog

examples/api/crt0.S

@@ -29,15 +29,17 @@ syscall:
 	.text
 	.globl _start
 _start:
-	ldr	ip, =search_hint
-	str	sp, [ip]
+	ldr	r4, =search_hint
+	mov	r5, sp
+	str	r5, [r4]
 	b	main
 
 
 	.globl syscall
 syscall:
-	ldr	ip, =syscall_ptr
-	ldr	pc, [ip]
+	ldr	r4, =syscall_ptr
+	ldr	r4, [r4]
+	bx	r4
 
 #elif defined(CONFIG_ARM64)