ps3-dump-bootloader: Remove bash specific code

Signed-off-by: Geoff Levand <geoff@infradead.org>
diff --git a/ps3-dump-bootloader.in b/ps3-dump-bootloader.in
index 51b7799..a2eaf0f 100644
--- a/ps3-dump-bootloader.in
+++ b/ps3-dump-bootloader.in
@@ -77,7 +77,7 @@
 	exit 1;
 fi
 
-let ldr_offset=512*ldr_offset
+ldr_offset=$((512 * ldr_offset))
 
 if [ "$sum" ]; then
 	dd if=/dev/ps3flash bs=1 skip=$ldr_offset count=$ldr_size | md5sum