powerpc/head_check: Fix shellcheck errors

Replace "cat file | grep pattern" with "grep pattern file", and quote a
few variables. Together that fixes all shellcheck errors.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210817125154.3369884-1-mpe@ellerman.id.au

arch/powerpc/tools/head_check.sh

@@ -49,11 +49,11 @@ vmlinux="$2"
 $nm "$vmlinux" | grep -e " [TA] _stext$" -e " t start_first_256B$" -e " a text_start$" -e " t start_text$" > .tmp_symbols.txt
 
 
-vma=$(cat .tmp_symbols.txt | grep -e " [TA] _stext$" | cut -d' ' -f1)
+vma=$(grep -e " [TA] _stext$" .tmp_symbols.txt | cut -d' ' -f1)
 
-expected_start_head_addr=$vma
+expected_start_head_addr="$vma"
 
-start_head_addr=$(cat .tmp_symbols.txt | grep " t start_first_256B$" | cut -d' ' -f1)
+start_head_addr=$(grep " t start_first_256B$" .tmp_symbols.txt | cut -d' ' -f1)
 
 if [ "$start_head_addr" != "$expected_start_head_addr" ]; then
 	echo "ERROR: head code starts at $start_head_addr, should be $expected_start_head_addr" 1>&2
@@ -63,11 +63,11 @@ if [ "$start_head_addr" != "$expected_start_head_addr" ]; then
 	exit 1
 fi
 
-top_vma=$(echo $vma | cut -d'0' -f1)
+top_vma=$(echo "$vma" | cut -d'0' -f1)
 
-expected_start_text_addr=$(cat .tmp_symbols.txt | grep " a text_start$" | cut -d' ' -f1 | sed "s/^0/$top_vma/")
+expected_start_text_addr=$(grep " a text_start$" .tmp_symbols.txt | cut -d' ' -f1 | sed "s/^0/$top_vma/")
 
-start_text_addr=$(cat .tmp_symbols.txt | grep " t start_text$" | cut -d' ' -f1)
+start_text_addr=$(grep " t start_text$" .tmp_symbols.txt | cut -d' ' -f1)
 
 if [ "$start_text_addr" != "$expected_start_text_addr" ]; then
 	echo "ERROR: start_text address is $start_text_addr, should be $expected_start_text_addr" 1>&2