mfd: fix comment

Signed-off-by: Antonio Ospite <ao2@ao2.it>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/mfd/intel_msic.c

@@ -27,7 +27,7 @@
 
 /*
  * MSIC interrupt tree is readable from SRAM at INTEL_MSIC_IRQ_PHYS_BASE.
- * Since IRQ block starts from address 0x002 we need to substract that from
+ * Since IRQ block starts from address 0x002 we need to subtract that from
  * the actual IRQ status register address.
  */
 #define MSIC_IRQ_STATUS(x)	(INTEL_MSIC_IRQ_PHYS_BASE + ((x) - 2))