Tegra: T30: Beaver: Fix board/board_name env vars, s/b beaver, not cardhu

Did a 'strings u-boot-dtb-tegra.bin | less' and saw that both
board and board_name == beaver. Didn't test as I have no T30
Beaver board here.

Signed-off-by: Tom Warren <twarren@nvidia.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
diff --git a/boards.cfg b/boards.cfg
index d2faf07..33e7549 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -325,7 +325,7 @@
 ventana                      arm         armv7:arm720t ventana           nvidia         tegra20
 whistler                     arm         armv7:arm720t whistler          nvidia         tegra20
 cardhu                       arm         armv7:arm720t cardhu            nvidia         tegra30
-beaver                       arm         armv7:arm720t cardhu            nvidia         tegra30
+beaver                       arm         armv7:arm720t beaver            nvidia         tegra30
 dalmore                      arm         armv7:arm720t dalmore           nvidia         tegra114
 colibri_t20_iris             arm         armv7:arm720t colibri_t20_iris  toradex        tegra20
 u8500_href                   arm         armv7       u8500               st-ericsson    u8500