git-prompt: make __git_eread intended use explicit

__git_eread is used to read a single line of a given file (if it exists)
into a single variable stripping the EOL.
This patch removes the unused capability to split file contents into tokens
by passing multiple variable names. Add a comment and explicitly use $2
instead of misleading $@ as argument to the read builtin command.

Signed-off-by: Robert Abel <rabel@robertabel.eu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-prompt.sh

@@ -278,11 +278,12 @@ __git_ps1_colorize_gitstring ()
 	r="$c_clear$r"
 }
 
+# Helper function to read the first line of a file into a variable.
+# __git_eread requires 2 arguments, the file path and the name of the
+# variable, in that order.
 __git_eread ()
 {
-	local f="$1"
-	shift
-	test -r "$f" && read "$@" <"$f"
+	test -r "$1" && read "$2" <"$1"
 }
 
 # __git_ps1 accepts 0 or 1 arguments (i.e., format string)