ARM: dts: NSP: Fix mpcore, mmc node names

Running dtbs_check yielded the issues with bcm-nsp.dtsi.

Firstly this patch fixes the following message by appending "-bus" to
the mpcore node name:
mpcore@19000000: $nodename:0: 'mpcore@19000000' does not match '^([a-z][a-z0-9\\-]+-bus|bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'

Secondly mmc node name. The label name can remain as is.
sdhci@21000: $nodename:0: 'sdhci@21000' does not match '^mmc(@.*)?$'

Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>