trivial: fix an -> a typos in documentation and comments

It is always "an" if there is a vowel _spoken_ (not written).
So it is:
"an hour" (spoken vowel)
but
"a uniform" (spoken 'j')

Signed-off-by: Frederik Schwarzer <schwarzerf@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/acpi/executer/exresolv.c b/drivers/acpi/executer/exresolv.c
index 89571b9..60e8c47 100644
--- a/drivers/acpi/executer/exresolv.c
+++ b/drivers/acpi/executer/exresolv.c
@@ -146,7 +146,7 @@
 
 	stack_desc = *stack_ptr;
 
-	/* This is an union acpi_operand_object    */
+	/* This is a union acpi_operand_object    */
 
 	switch (ACPI_GET_OBJECT_TYPE(stack_desc)) {
 	case ACPI_TYPE_LOCAL_REFERENCE: