generic: 5.15: enable Werror by default for kernel compile

From 5.15 and up linux kernel introduced CONFIG_WERROR to flag any
warning as error. To improve code quality, enable this by default to
catch any warning and fix it.

Signed-off-by: Christian Marangi <[email protected]>

target/linux/generic/config-5.15

@@ -7467,7 +7467,7 @@ CONFIG_WATCHDOG_OPEN_TIMEOUT=0
 # CONFIG_WD80x3 is not set
 # CONFIG_WDAT_WDT is not set
 # CONFIG_WDTPCI is not set
-# CONFIG_WERROR is not set
+CONFIG_WERROR=y
 # CONFIG_WEXT_CORE is not set
 # CONFIG_WEXT_PRIV is not set
 # CONFIG_WEXT_PROC is not set