[ARM] Storage class should be before const qualifier

The C99 specification states in section 6.11.5:

The placement of a storage-class specifier other than at the beginning of the
declaration specifiers in a declaration is an obsolescent feature.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>