linux-firmware: Fix SRCURL

Fix up the unwanted substitution of 0.

```
$ beeversion linux-firmware-0_t1449454640_bbe4917-0.bee
PKGNAME=linux-firmware
PKGEXTRANAME=
PKGEXTRANAME_UNDERSCORE=
PKGEXTRANAME_DASH=
PKGVERSION=( 0 0 )
PKGEXTRAVERSION=t1449454640_bbe4917
PKGEXTRAVERSION_UNDERSCORE=_t1449454640_bbe4917
PKGEXTRAVERSION_DASH=-t1449454640_bbe4917
PKGREVISION=0
PKGARCH=
PKGFULLNAME=linux-firmware
PKGFULLVERSION=0_t1449454640_bbe4917
PKGFULLPKG=linux-firmware-0_t1449454640_bbe4917-0
PKGALLPKG=linux-firmware-0_t1449454640_bbe4917-0
PKGSUFFIX=.bee
```

linux-firmware-0_t1449454640_bbe4917-0.bee

@@ -13,7 +13,7 @@
 ## The source URL(s) define the location of the sources that will be
 ## downloaded. Version variables may be used to simplify reuse of this bee-file.
 
-SRCURL[${PKGVERSION}]="/src/mariux/beeroot/downloads/linux-firmware-${PKGVERSION}_t144945464${PKGVERSION}_bbe4917.tar.bz2"
+SRCURL[0]="/src/mariux/beeroot/downloads/linux-firmware-0_t1449454640_bbe4917.tar.bz2"
 
 ###############################################################################
 ## Add URLs/pathes to patch files to the PATCHURL array.