x86/boot: Repair kernel-doc for boot_kstrtoul()

Adjust the kernel-doc comment to have the proper function name:
boot_kstrtoul().

  [ bp: Massage commit message. ]
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221031094835.15923-1-lukas.bulwahn@gmail.com

arch/x86/boot/string.c

@@ -350,7 +350,7 @@ static int _kstrtoul(const char *s, unsigned int base, unsigned long *res)
 }
 
 /**
- * kstrtoul - convert a string to an unsigned long
+ * boot_kstrtoul - convert a string to an unsigned long
  * @s: The start of the string. The string must be null-terminated, and may also
  *  include a single newline before its terminating null. The first character
  *  may also be a plus sign, but not a minus sign.