[ARM] 5232/1: Do not post-index STRT instruction in clear_user.S

The last strnebt instruction has a post-index of 1 but the address
register is set to 0 in the next instruction, so no need for
post-indexing.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>