linux-gbmc: Fix FLASH_LAYOUT_SIZE size check

Make sure the flash size check is done properly to prevent the issue
where all system are running with gbmc-flash-layout-64.dtsi.

Tested:
On a gBMC with FLASH_SIZE of 32768.
```
$ cat ./tmp/work-shared/gbmc/kernel-source/arch/arm/boot/dts/npcm7xx-gbmc.dtsi
                #include "gbmc-flash-layout-32.dtsi"
```

Google-Bug-Id: 383236243
Fusion-Link: fusion2 N/A. This reverts back to the expected layout.
Change-Id: I603e69f9d8115772d1dc142e58ae00b5bef1fd18
Signed-off-by: Willy Tu <wltu@google.com>
Platforms-Affected: 32MB FLASH size systems
(cherry picked from commit 5a38c29e42af6fd89fca5080c24a54f7cf7663eb)
diff --git a/recipes-kernel/linux/linux-gbmc.inc b/recipes-kernel/linux/linux-gbmc.inc
index 017c502..48370f8 100644
--- a/recipes-kernel/linux/linux-gbmc.inc
+++ b/recipes-kernel/linux/linux-gbmc.inc
@@ -88,7 +88,7 @@
 # We only have a special flash layout for 32MB platforms, the 64MB layout is
 # generic and should be used by all other sized flashes with dynamic image
 # support turned on.
-FLASH_LAYOUT_SIZE = "${@32 if d.getVar('FLASH_SIZE') == 32768 else 64}"
+FLASH_LAYOUT_SIZE = "${@32 if d.getVar('FLASH_SIZE') == '32768' else 64}"
 
 do_ksrc_splice() {
   # Ensure that our SPI override file is correctly in place over a valid file in the tree