[MIPS] pte_offset(dir,addr): parenthesis fix

This patch adds missing parenthesis around 'dir' argument in pte_offset()
macro definition.

It also removes an extra space in the definition of pte_offset_kernel()
macro.

Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>