powerpc: Fix a typo in comments of va to pa conversion

This patch fixes typo in comments virtual to physical
address conversion.
Signed-off-by: NVaishnavi Bhat <vaishnavi@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/page.h

@@ -78,7 +78,7 @@ extern unsigned int HPAGE_SHIFT;
  *
  * Also, KERNELBASE >= PAGE_OFFSET and PHYSICAL_START >= MEMORY_START
  *
- * There are two was to determine a physical address from a virtual one:
+ * There are two ways to determine a physical address from a virtual one:
  * va = pa + PAGE_OFFSET - MEMORY_START
  * va = pa + KERNELBASE - PHYSICAL_START
  *