checkpatch: fix incorrect camelcase detection on numeric constant

checkpatch: fix incorrect camelcase detection on numeric constant

The code fragment below

	int foo(int *array, int index)
	{
		return array[index & 0xFF];
	}

triggers an incorrect camelcase detection by checking a substring of the
hex constant:

	CHECK: Avoid CamelCase: <xFF>
	#3: FILE: test.c:3:
	+	return array[index & 0xFF];

This is caused by passing the whole string "array[index & 0xFF]" to the
inner loop that iterates over a "$Ident" match.  The numeric constant is
not a $Ident as it doesn't start with [A-Za-z_] and should be excluded
from the match.

Similar issue can be detected with other constants like "1uL", "0xffffU".

Force the match to start at word boundary so the $Ident will be properly
checked starting from its first char and the constants will be
filtered-out.

Link: https://lkml.kernel.org/r/20220613100055.77821-1-borneo.antonio@gmail.com
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>