ARC: pgalloc.h: delete a duplicated word + other fixes

Drop the repeated word "to".
Change "Thay" to "That".
Add a closing right parenthesis.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: linux-snps-arc@lists.infradead.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>